Coronaless shockproof unit



Dec. 4, 1934. M, MORRISON CORONALESS SHOCKPROOF UNIT Filed June l, 1932 ILI ,i v lill |m.\ Y wh mm. QM. m Q Y H W .Q H I .U I|| .v H m Mm w m 0 I I Patented Dec. 4, 1934 vUNl'l-l-:D STATES l 1,982,825 conoNALEss sHocKPRooF UNIT Montford Morrison, Montclair, NQJ., assignor to Westinghouse X-Ray Company, Inc., a corporation of Delaware Application June 1, i932, semi No. 614,738

E s claims.k (c1. 25o-34) My invention relates to shookproof apparatus utilized with discharge devices, such for example as Xray tubes which are subjected to relatively high potential electrical energyjbetween the electrodes thereof without danger of possible shocks or disturbing noises which are detrimental to the operator or patient. y Y' Apparatus of this general type are well known to the art and in such apparatus the high potential source of energy and the discharge device are usually immersed in a cooling and insulating medum within a metallic container. ductors and high tension terminals lare thus immersed in the insulating medium which prevent contact thereof by operator or patient; By immersing the tube in the insulating' and cooling medium it naturally follows that the requisite spacing between all high tension carrying parts can be materially lessened for the operating voltvages of the tube than that normally required for this liquid medium over a gaseous medium, such as air.` f f requiring replacement thereof itis necessary to disconnect the conductorsvfrom the X-ray tube terminals while they are immersed in the oil and handle the oil coated tube. This at best'is-an unpleasant and time consuming task and usually requires the services of a skilled mechanic as the operator, who, is in most instances a Rentgenologist, is unfamiliar with these internal connections.

sults in a puncture of the glass envelope causing particles thereof to fall uponthe transformer it is necessary to drain off the insulating `and coolin medium to remove all these particles. Y

. A structure retaining all the advantagesv of these well knowntypes of apparatus while obviating the objectionable features thereof has been disclosed in the c'opending application ofc W. A. McKay, Serial No. 572,785, filed November aspect relates to such types of shockprooffapparatus and is in the nature of an improvement thereon. In `this particular vstructure thezhigh` tension source of energy is immersed in a liquid` cooling and insulating material whereas the discharge device, such as an X-ray tube, is surrounded by a gaseous insulating material, such as'air. ff Although the shortestspaeing, or normal `arn- All the conf l" objectionablefeatures, howevenexist, in, such apparatus in that upon failure1 of the yX-ray,t.l .iloe

Moreover, if failure of the device ref k3., 1931, and my present invention in'its broadest Y" bient medium gap,between the electrodes ofthe;

X-r'ay tube, measured.outside the tube, is less than that required for the voltages at which the tube is designed to operate, the critical ambient ing vvoltages of the tube. By the novel construction of this apparatus sparkover between the terminals 'of the tube and all hightension parts is 'prevented resulting in a simple, compact, shock- .proof unit.

In this particular apparatus, as shown in the above mentioned copending application, the X- ray tube isprovided with certain baffles or elec- .trlcal barriers which are intermeshed with the yelectrical barriers, forming part of a hollow open vase shaped receptacle forV the X-ray tube.

This structureconsiderably increases the length offthe'" free` air` 'gap' sparkover distance or, as

ergizing transformer. Due to the difference in dielectric strength between the electrical barriers, the 'air-spaced jacket and the liquid ditherein termed, -""thecritical ambient medium A gap, between the anode stem, whichuprojects `outside the'glafss envelope of the X-ray tube, and y the cathode connections. lThe envelope of the .hX-ray tube is effectively surrounded by an air spacedvjacket and,"arou'nd this jacket, is conltained the oil immersing the high tension enelectric immersing the transformer and surrounding the'airespaced jacket, the potential gradient at certain points in these various dielectric `media is considerably increased resulting in the formation of corona Aat these points during operation of the device, which is annoy--` ing tov operator and patient.

It is accordingly an object of my invention to o fix thefpotential at or near the surface dividing the 4.dielectric media 'so that the gaseous insulat" ing medium surroundingk the X-ray tube will not be overstressed and theformation of corona will medium having a specific dielectric strength,

with the source of high tension energy for energizing the tube disposed in an ambient medium having a higher dielectric strength than the ambient medium for said tube, in which a dielectric member separates the two ambient media and in which the formation of corona is prevent- #ed despite the difference in dielectricl strength of the various ambient media.

Another object of my invention is to provide a shockproof X-ray apparatus embodying an X-ray tube surrounded by a gaseous insulating medium wherein the spacing between the electrodes thereof is insufficient to prevent spark over at the operating potential of the tube in which the spacing therebetween `is increasedY upon insertion of the tube inthe apparatus to prevent spark over during operation and in which the formation of corona is prevented.

A further object of my invention is the pro-` vision of a shockproof X-ray apparatus utilizing K an X-ray tube having electrodes spaced apart a distance less than that required therefor when operating at its working potential in a gaseous insulating medium in which insulating baille's are employed of a higher dielectric strength than the gaseous insulating medium, to increase the critical ambient gap, to prevent spark over` in that medium at the operating potential of the` tube and in which the formation of corona -is prevented despite the differences in dielectric strength of the various insulating media.

A further object of my invention is the provision of a shockproof X-ray apparatus employing an X-ray tube having electrodes spaced apart a distance less than that necessary when operating at the working potential of the tube in a gaseous insulating medium in which means are utilized having a higher dielectric strength than the gaseous insulating medium to increase the critical ambient gap to prevent spark over` between the electrodes in a gaseous medium, at the operating potenial ofthe tube, and in which the potential gradient at the points of greatest stress is materially reduced to prevent the formation of corona. y f A* l Still further objectsof my invention will become apparent to those skilled? inthe art by ref- *l `Figure 2 is a cross-sectional view of the struceture of my apparatus shown in Fig. 1, taken on the line II-II thereof. .f

Referring now to the drawing in detail I have shown a metallic casing or tank 5, which con` tains a body of liquid insulating ambient material 6, such for example as oil. rA cup-shaped member 7, composed of a suitable dielectric ma terial, such as hard rubber, glass, porcelain or a phenolic condensation product, extends invwardly of the casing top and is thus surrounded by the liquid insulating medium therein. This cup-shaped dielectric member '7 has a cylindrical or conical wall 8 having a flange 9 extending outwardly therefrom at the upper end for the purpose lof supporting the member in the casing and also to form an oil tight seal't'herefkor.

An electrical conducting socket 10- is molded or otherwise secured in the base of the dielectric member 7 and is provided with a suitable opening centrally disposed thereof into which extends a suitable heat conducting stem or rod 12. A cooling radiator 13 is rigidly secured to the lower extremity of this socket by means of a screw 14 and suitable washers 15.k

The base of the cup-shaped dielectric member 7 is further provided with a pair of upwardly extending spaced concentric cylindrical baile members 16 and 17, of the same material as the member 7, which may be molded integral therewith. These bales are of varying length, with the axes thereof in alignment with the stem 12 and opening in the conducting socket 10, for a purpose to be hereinafter more fully set forth.

An X-ray tube 18, considerably shortened in length, is disposed interiorly of the cup-shaped dielectric member 7 and is of general cylindrical form with a'substantiallyhemispherical upper end 19. The lower end of this X-ray tube is provided with'a vre-entrant sleeve 20 extending upwardly within and spaced from the main body portion of the X-ray tube. A metallic tubular sleeve member 22 is sealed to the upper portion of this re-entrant sleeve and in turn supports an anode 23 internally of the X-ray tube. This anode is arranged to en gage'theheat conducting stem 12 in any suitable manner, such for example, as threadedly engaging the latter or by the provision of a tapered recess portion of vthe anode engaging an upper reduced diameter, tapering extremity provided on the stem 12, which extends through the inner spaced surrounding cylindrical balal, for the purpose of transmitting the heat from Athe anode to the cooling radiator 13. j A tubular metallic skirt k24 is likewise supported by the sleeve 22 spaced therefrom, which extends downwardly below the glassmetal seal formed bythe re-entrant sleeve and the metallic sleeve 2,2.

A second re-entrant` tube 25 is sealed internally of the X-ray tube 18 at a point slightly below the metaleglass seal and at its upper extending portion, the greater part of which is spaced from the walls rof thetube 18, supports a spring sleeve 26 Vfirmly secured to the anode, for the purpose of additionally supporting the anode and serving as a shock absorber.Y A glass cylinder 27, which may be suitably fused to the exterior of the X-ray tube', extends downwardly a substantial distance of the tube with the lower extremitythereof in, alignmentA erence to the accompanyingk drawing, wherein ,'.Wlth "he lqwel'vend of the tube- Figure 1 is a cross sectionalview o f my novel` tors therefor are'sfecu'red to terminal caps 23 dis posed-exteriorly of the tube. A low tension translformer immersed in the liquid insulating medium randi'sljiow'n diagrammatically at 29 has its second- Darywln'f'zlirig 30 connected to these terminal caps 28` by means of a pair of conductors 32 and 33, one of which extends through an insulating bushing 34m the wall of the cup-shaped member 7, and theother 'of which is suitably grounded to the casing 5 at 35, passing iin-insulated through the wall ofI the member 7, for a purpose hereinafter explained.

A high tension transformer 36, also immersed in the liquid insulating medium, is provided with two secondary windings 3'7 and 38 connected in series for supplying high tension electrical energy to the main electrodes of the X-ray tube 18, through a conductor 39, which is connected to the anode 23 through the radiator 13, and a conductor 40, which is connected vto the conductor' 33 and zthusgrounded vat 35, connects the secondary windings of the usual commercial potential (not shown) by having the supply conductors therefor extended exteriorly of the casing 5 in any suitable manner, such for example, as'a terminal block (not shown) In order to protect the X-ray tube 18 from 'breakage I provide the dielectric cup-shaped member 7 with a cap 44 formed of a phenolic condensation productor any other suitable material,

A thermionic cathode (not shown.) vis providedv interiorly of the tube 18 and the lead-in conduciso over the upper hemispherical end V19 of the tube which may be secured to the flange portion ofthe cup-shaped member.` Although the cup-shaped member '7 and the oil within the casing absorbs substantially all stray X radiation, a lead band,

is preferably secured to the inner sideof the cap 44 and extends slightly downwardly to overlap the upper portion of the cup-shaped member 7. The insulating bushing 34 prevents contact .of the conductor 32 with the groundedlead band 45, whereas. the conductor 33 passes uninsulated through the cup-shaped member 'land lead band 45 to properly ground the latter to the casing. 5.

The X-ray tube, as hereinbefore stated, is con.- siderably shortened in length; i. e., v'the normal spacing or ambientV medium gap between theelec.-`

trodes measured outside the tube, as shown by the dotted line in Figi, is insufficient to -prevent spark over therebetween in the gaseous insulating medium, at the operating potential of the tube.

When,.however, the` tube isfpositioned within the cup-shaped member 7,the baffles 16 and 17,

infcooperation with the glasscylinderor skirtz2'l baffles, together with the gaseous insulating me# diurn,Y such. as the air surrounding Athe tube,V is thus sufficient to prevent spark overfbetween the electrode terminals at the maximum operating potentials of the tube. f

It isto be understoodthat although I have shown and described an X-ray tube, considerably shortened in length, which is operable at `a'po-V tential above that required to cause `spark over between the electrode terminals, whereindielectriebaiiles are provided `to increase'thecrtical gaseous ambient medium gap to Lan, extent; preferably greater than that required to prevent spark over between the electrodes, rit follows thatthe X-ray tube may be operated atlower potentials without the necessity of these baies` or barriers',v provided the Spark over distance at these lower potentials is less than the normal spacing'between the electrode terminals-of theX-ray tube.

The portion' of my invention thus far described is substantially analogous to that shownandde-- member and the copper rod cr stern 12 a gaseous insulating medium, such as air, utilized with the bailies 16 and 17 interposed therebetween` thus constituting two further insulating media of different dielectric strengths.

Although I have shown the high and low ten` polarity is prevented.

This maybe appreciated sion .transformers 36 and 29 diagrammatically. in

the actual embodiment of my invention the iron core of each, together with their respective windings, utilize substantially all ofthe spacing between theinner wall of the casing 5 and the cupshaped-member '7, in order to conserve space and make the entire unit as compact as possible.

The ironicores of these transformers are also groiuidedl to the casing and thus carry ground potential-.with 'itha spacing `between them and the copper stem or rod 12 materially reduced, with the aforementioned dielectric media interposed therebetween. It can, therefore, be appreciated that a. relatively strong electrostatic field is created withthe potential gradient strongest at various points in the dielectric insulating members. For example, the potential gradient in the outer wall of thecup-shaped member '7 will be relatively large at points in close proximity to the grounded iron cores of the transformers and the copperfanode 4stem or-rod` 12, `which are designatedfat A in Fig. 1.- l Y There is also alarge potential gradient at points electrostaticI eld andr the difference in dielectric strength'- of this insulating bafe and thel sur--l rounding-gaseous insulating medium, such as air. Likewise an equally strong potential gradient is imposed-'at points C in the inner cylindrical baffle member 16.-

Although as before stated the spacing between the anode stem`12 and the high potential cathode terminal28, `with theX-ray tube in position, is greatvenough'tomake the `critical ambient medium'g'ap; as shown by the dot anddash line in the' figure, sufc'ient to prevent spark over therebetween at operating voltages of the tube, the strong potential gradient at certain points in the 'varousgdielectric'members may cause the forma" tion of Y corona atjthese points.

In orderwto entirely eliminate the formation of coronaIsuri-'ound the cup-shaped dielectric Amember 7' with'a rnetalliccylindrical sleeve or-collar of uniform diameter,` or which may follow the` contour `of the tapering walls 8. This sleeve constitutes'a potential divider and extends a substantial distance longitudinally ofthe cup-shaped dielectric memberr 7 with the lower end preferably slightly-below 'the latter member. The upper 4 andflowerendsof this sleeve are provided with a rounded edge52, which may be rolledor otherwise suitably formed to obviate sharp edges and points. A plurality of insulatedwedges such as shown at 53, may` be utilized to secure the sleeve membrf50 about y the lower periphery of the cupshaped member, thus allowing a slight nlm of oil therebetween or, if desired, the sleeve may be rigidly-affixed directly to the cup-shaped member. t

In a similar'manner smaller insulated wedges 54 may be employed at the upper end of the sleeve member 50' to assist in'securing the latter to the cup-shaped member.`

For the lpurpose of reducing the potential gradient at the points of greatest stress in the various dielectric members, namely A, B, and` C, I connected this potential dividing sleeve 50 tothe sec.

ondary winding of the high tension transformer 36 by meansro'f a conductor 55. Although inthe embodiment of my invention, shown in the accompanying drawing, I have shown the conductor 55 connected to the mid-point between the two secondary windings 37 and 38, and substantially one halfV the total output'potential of these windingsis impressed between the sleeve 50.v and both the anode and ground, thus-substantially divid- 15ml tube is the salient factor that controls the requisite potential which must be applied between the sleeve 50 and the anode stem l2 to prevent the formation of corona. It necessarily follows that the greater the operating potential of the tube 4the greater the potential which must be impressed upon the sleeve 50.

In applying a given potential to this sleeve 50 the potential gradient at the points of greatest stress in the various dielectric insulating-media are reduced in proportion to the difference between the total output potential of the entire secondary winding of the high tension transformer and that between the sleeve 50 and the anode stem l2. f

In impressing a predetermined definite potential upon the sleeve 50 the potential gradient at the normalpoints of greatest stress, namely A,

B and C, will be no greater than the potential between the anode stem 12 and the sleeve 5D. The operating potential of the X-ray tube andthe length of the critical ambient mediumgap required to prevent spark over` between the electrodes of the tube is accordingly immaterial and does not affect the potential gradient, which asl previously mentioned,ris nxed'by the sleeve 50.

This may be best appreciated by assuming given potential values. Assumingtherefore, that the` total operating potential of the X-ray tube andy consequently theoutput of the secondary windings is 100 k.v. with the sleeve 50 connected, by means of conductor 55, to the midpoint between these windings, as shown in the figure, a potential of one-half the total operatingv potential of the tube is thus impressed between the sleevey 50 and the anode stem l2, and between the for-` mer and the grounded casing 5. The electrostatic eld and the stress upon the various dielectric insulating media is accordingly reduced by a reduction in potential between sleeve 50 and anode stem l2 to 50 k.v. The points in these various dielectric media of greatest potential stress are likewise reduced to a value of 50 k.v. which is more than sufficient to prevent the formation of corona at these points.

If now the conductor 55 is connected to eithe one of the respective rwindings in such .a manner that, with the operating potential of the X- ray tube being 100 l .v., only 40 k.v. is impressed between the sleeve 50 and the anode stem l2, while 60 k.v. is impressed between the sleeve and ground. ,Again the potential gradient at the points of greatest stress in the dielectric insulating media is reduced to a potential which is sufficient to prevent the formation of corona at these points.

It naturally follows that there is a certain minimum beyond which the potential impressed upon the sleeve 50 cannot be reduced at a given operating potential of the X-ray tube without corona forming at the points of greatest potential stress in the dielectric media. This, as before stated, depends primarily on the operating potential of the X-ray tube and with a lowering of the same this minimum potential necessary -for the sleeve 50 is also lowered. y l

Moreover, it is not essential that the potential dividing sleeve 50 be connected to the high voltage source by a conductor as it will assume a definite potential under operation. In order, however,

4for this sleeve to assume a requisite potential sufficient to prevent the formation of corona the various parts must be properly proportioned. The 'liquid' dielectric surrounding the high tension transformer 36 and the cup-shaped member` 7 has a specific dielectric strength as well as the gaseous insulating medium surrounding the X- raytube. l A difference in dielectric strength likewise exists in the baflles or barriers 16 and 17, as

before stated. This, therefore, causes these various dielectric media to act in a manner analogous to condensers connected in series, i. e., the casing wall and the member 7 constitutes one condenser and the latter member, together with theftube `surrounded by the gaseous insulating medium, constitutes the other condenser.

However, as two dielectric media are involved, which differ in dielectric strength, the capacity effect of the same also differs. In the same manner as with condensers, therefore, the potential thereof will vary inversely proportional to the capacity.

For example, the liquid insulating medium having the largest capacity effect will cause a greater potential stress to be' electrostatically impressed upon the interior of the cup-shaped member 7 and the baflies 16 and 17 than upon the casing walls and the exterior of the cupshaped member 7, in contact with the oil. The potential divider sleeve 50 being positioned as a plate in one of these fictitious condensers will,

therefore, assume a definite potential by induc- .tion from 4the source of energy for the tube.

In order forlthisy potential to beV inductively impressed' upon the sleeve 50 sufiicientlyfgreat enough to vvprevent the formation of corona, as before mentioned, during operation of the device its 4spacing relative to the cup shaped member must be apportioned to the operating potential kof the 'Y -ray tube and the capacity effect createdby the-gaseous insulating medium forming the remaining fictitious condenser. This can, however, be readily calculated or may be done empirically until there is an entire absence of the formation of corona at the maximum operating potential of the X-ray tube.

It thus becomes obvious to those skilled in the vart that I have provided a novel shockproof unit utilizing an X-ray tube in a gaseous insulating medium, considerably shortened in length, wherein the spacing ornormal ambient medium gap between the electrodes is less than that required at the operating potential of the tube in that medium and in which the critical ambient mediuml gap is rendered sufficient to prevent spark over between the electrodes by the utilization of dielectric insulating media of varying dielectric strength and the formation of corona is an envelope and electrodes spaced apart and disposed in an ambient dielectric medium, means disposed vin said casing in a second ambient dielectric medium in juxtapositiony with said discharge device for energizing said discharge device and having portions thereof in close proximity to the latter, dielectric means 4disposed .between said discharge device and said rst mentioned means to prevent contact of the respective ambient dielectric media for each and forming a compartment for housing saiddischarge device, and means disposed inthe shortest path between said dielectric means and said first mentioned means to reduce the potential gradient upon said dielectric means and the ambient dielectric medium for said discharge device and said rst mentioned means, respectively, at points of greatest potential stress, and to prevent the formation of corona between said discharge device and all parts of said rst mentioned means disposed in close proximity to said discharge device.

2. In an X-ray apparatus the combination of a casing, an electrical discharge device having an envelope and high tension electrode terminals spaced apart a distance less than that required to prevent spark over therebetween at the operating potential of said device, means 'carried by said casing and cooperating with said discharge device to increase the spark over distance between the electrodes of said device to an extent at least as great as that required to prevent spark over therebetween at the maximum operating potential of said device and forming a housing for said discharge device, means in said casing in juxtaposition with said rst mentioned means and connected to said .discharge device for energizing the same, and

tioned means to prevent the formation of corona v about said rst mentioned means and said discharge device.

3. In an X-ray apparatus the combination of a casing, an electrical discharge device disposed in an ambient dielectric medium and having an envelope and electrodes spaced apart a distance less than that required to prevent spark over therebetween at the operating potential of said device in said ambient medium, a second ambient dielectric medium in said casing having a higher dielectric strength than said rst mentioned ambient medium cooperating with the latter and said discharge device to increase the spark-over distance between the electrodes of said device to an extent at least as great as that required to prevent spark over at the maximum operating potential of said device and forming a housing for said discharge device, means disposed in said casing in a third ambient dielectric medium in juxtaposition to said second mentioned ambient dielectric medium and connected to said discharge device for energizing the latter, and means connected to said last mentioned means and surrounding said second mentioned ambient dielectric medium to reduce the potential gradient in all of said ambient dielectric media at points of greatest potential stress and to prevent the formation of corona between said discharge device and all said ambient dielectric media.

4. In an X-ray apparatus the combination of a casing, an electrical discharge device disposed in a gaseous dielectric insulating medium and having an envelope and high tension electrode terminals spaced apart a distance less than that required to prevent spark over therebetween at the operating potential of said device, a solid insulating medium in said casing having ahigher dielectric strength than said gaseous insulating medium cooperating withv said discharge device and said gaseous insulating medium to increase the?.

spark over distance between the electrodes of saiddevice to an extent at least as great as that required to prevent spark over at the maximum operating 'potential of said deviceand forming a housing ,for said dischargedevice, a high tension transformer in said 'casing immersed in a liquid insulating medium in juxtaposition with said solid contained therein and an ambient dielectric medium for said transformer, of a dielectric member extending into said casing in proximity to said transformer and forming a separate compartment provided with a gaseous ambient dielectric medium, a discharge device mounted in the ambient medium within the compartment formed by said dielectric member and connected to said transformer forlenergization by the latter, and means Adisposed in said casing between said transformer Vand saiddielectric member to reduce the potential gradient in said dielectric member and the ambient dielectric media for said transformerfand discharge device and to prevent the formation of corona during operation of said apparatus.

6. In an X-ray apparatus the combination with a transformer casing, a high tension transformer contained therein and an ambient dielectric medium for said transformer, of a dielectric member extending into said casing in proximity to said transformer and forming a separate compartment provided with a gaseous ambient dielectric medium, a discharge device mounted in the ambient medium within the compartment formed by said dielectric member and connected to said transformer for energization by the latter, and a metallic shield disposed in said casing between said transformer and said dielectric member and connected to the former to reduce the potential gradient in said dielectric member and the ambient dielectric media for said transformer and discharge device and to prevent the formation of corona during operation of said apparatus.

7 In an X-ray apparatus the combination with a transformer casing, a high tension transformer contained therein and an ambient dielectric medium for said transformer, of a dielectric member extending into said casing in proximity to said transformer and forming a separate compartment provided with a gaseous ambient dielectric medium, a discharge device mounted in the ambient medium within the compartment formed by said dielectric member and connected to said transformer for energization by the latter, and a metallic shield disposed in said casing between said transformer and said dielectric member, said metallic shield connected to said transformer to impress a potential thereupon less than the operating potential of said discharge device to reduce the potential gradient in said dielectric member and the ambient media for said transformer and discharge device, at points therein of greatest potential stress, to prevent the formation of corona about said discharge device duringoperation of said apparatus.

8. In an X-ray apparatus the combination with .a transformer casing, a high tension transformer contained therein and an ambient dielec- .tric medium for said transformer, of a dielectric member extending into the ambient mediumV for said transformer in proximity to the latter and forming a separate compartment provided with a gaseous ambient dielectric medium, a discharge device mounted in the ambient medium within the compartment formed by said dielectric member and connected to said transformer for energi- Zation by the latter, and means disposed in. said casing between said transformer and said de'lectric member, said means comprising a metallic shield connected to said transformer to form an electrostatic field less than the electrostatic field normally formed between said discharge device 

